1. Field of the Invention
The present invention relates to a driving control device, a power converting device, a method of controlling the power converting device and a method of using the power converting device which are suitable for use as an inverter, and more particularly to an improvement in suppression of the influence of a noise pulse with a switching operation of a power switching element.
2. Description of the Background Art
FIG. 5 is a circuit diagram showing a structure of a conventional driving control device to be the background of the present invention. A driving control device 151 is constituted by a high breakdown voltage integrating circuit and comprises a pulse generator 51, switching elements 52 and 53, resistive elements 58 and 59, a flip-flop circuit 54, switching elements 55 and 56, and an inverter element 57. The pulse generator 51 alternately sends a pulse to two outputs A and B synchronously with an input signal sent to a terminal HIN.
A series circuit of the switching element 52 and the resistive element 58 constitutes a level shift circuit. Similarly, a series circuit of the switching element 53 and the resistive element 59 constitutes another level shift circuit. The level shift circuits invert, level-shift and transmit the pulse output from the pulse generator 51 to the flip-flop circuit 54. The flip-flop circuit 54 is an RS flip-flop circuit, is set by a pulse sent to an input C and is reset by a pulse sent to an input D. The switching elements 55 and 56 and the inverter element 57 constitute a buffer circuit for amplifying an output signal of the flip-flop circuit 54 and outputting the amplified signal to a terminal HO.
When using the driving control device 151, a control electrode of a power switching element 71 is connected through the terminal HO to a connecting portion of the switching elements 55 and 56 which are connected in series. Impedances 73 and 74 may be connected to the control electrodes of the power switching element 71 and a power switching element 72. The power switching elements 71 and 72 are connected to each other in series. A load 81 is connected through a terminal OUT to a connecting portion of the power switching elements 71 and 72. An inductive load such as a motor is usually used for the load 81.
A power voltage of the pulse generator 51 is supplied from an external d.c. power supply connected to a terminal GND and a terminal Vcc. Power voltages of the flip-flop circuit 54, the switching elements 55 and 56 and the inverter element 57 are supplied through terminals VS and VB. The terminal VS is connected to the terminal OUT. A set of level shift circuits having the switching elements 52 and 53 and the resistive elements 58 and 59 are connected to the terminals GND and VB. Consequently, these level shift circuits convert a level of a signal having an electric potential of the terminal GND as a reference potential into a level of a signal having an electric potential of the terminal VS as the reference potential.
FIG. 6 is a timing chart showing a signal of each portion in an operation of the driving control device 151. In the following drawings, the designation of each portion in the device is exactly used as that of the signal in each portion. For example, the same designation xe2x80x9cHINxe2x80x9d is added to a signal input to the terminal HIN.
When the signal input to the terminal HIN rises to have a high level, a pulse having the high level is sent from the output A of the pulse generator 51 so that a pulse having a low level is sent to the input C of the flip-flop circuit 54. As a result, the flip-flop circuit 54 is set so that a signal of the terminal HO rises to have the high level. Consequently, the power switching element 71 is turned on. Correspondingly, a current I flowing in the power switching element 71 is started to be increased and a voltage VDS between a pair of main electrodes of the power switching element 71 is started to be dropped.
When the signal input to the terminal HIN falls to have the low level, the pulse having the high level is sent from the output B of the pulse generator 51 so that the pulse having the low level is sent to the input D of the flip-flop circuit 54. As a result, the flip-flop circuit 54 is reset so that the signal of the terminal HO falls to have the low level. Consequently, the power switching element 71 is turned off. Correspondingly, the current I is started to be decreased and the voltage VDS is started to be raised. Thus, the power switching element 71 is turned on and off synchronously with the signal input through the terminal HIN.
In the conventional driving control circuit 151, however, there has been a problem in that a noise pulse is induced to the input of the flip-flop circuit 54 with the switching operation of the power switching element 71 and the switching operation of the power switching element 71 is thereby influenced in some cases. FIG. 7 is a timing chart showing the signal of each portion in the device which is obtained when the power switching element 71 is turned on, illustrating the influence of the noise pulse.
When a pulse is sent to the output A, the power switching element 71 is turned on so that the voltage VDS is dropped. The drop in the voltage VDS implies a rise in the electric potential of the terminal VS. If a voltage of a power supply to be connected to the power switching elements 71 and 72 is 300 V, the electric potential of the terminal VS is raised from 0 toward 300 V. If a change rate dV/dt of the voltage VDS is great, a current flows through the terminal VS by the action of a floating capacitance present in the driving control device 151. As a result, the current flows through a parasitic capacitance of the switching element 53 so that a noise pulse having a low level is applied to the input D of the flip-flop circuit 54 in some cases.
When the noise pulse is applied to the input D, the flip-flop circuit 54 is reset. As a result, the signal of the terminal HO is returned to the low level so that the power switching element 71 is turned off. Consequently, the current I is started to be decreased so that the voltage VDS is started to be raised. More specifically, a normal turn-on operation of the power switching element 71 is blocked.
FIG. 8 is a timing chart showing a signal of each portion in the device which is obtained when the power switching element 71 is turned off, illustrating the influence of the noise pulse. When a pulse is sent to the output B, the power switching element 71 is turned off so that the voltage VDS is raised. The rise in the voltage VDS implies the drop in the electric potential of the terminal VS. If the voltage of the power supply to be connected to the power switching elements 71 and 72 is 300 V, the electric potential of the terminal VS is dropped from 300 V toward 0. If a change rate dV/dt of the voltage VDS is great, a current flows through the terminal VS by the action of a floating capacitance present in the driving control device 151. As a result, the current flows through a parasitic capacitance of the switching element 52 so that a noise pulse having a low level is applied to the input C of the flip-flop circuit 54 in some cases.
When the noise pulse is applied to the input C, the flip-flop circuit 54 is set. As a result, the signal of the terminal HO is returned to the high level so that the power switching element 71 is turned on. Consequently, the current I is started to be increased so that the voltage VDS is started to be dropped. More specifically, a normal turn-off operation of the power switching element 71 is blocked. In the conventional driving control device 151, thus, there has been a problem in that the influence of the noise pulse is caused with the switching operation of the power switching element 71 in some cases.
In order to eliminate the drawbacks of the conventional art, it is an object of the present invention to provide a driving control device, a power converting device, a method of controlling the power converting device and a method of using the power converting device which can suppress the influence of a noise pulse with the switching operation of a power switching element.
The present invention is directed to a driving control device for controlling a driving operation of a power switching element, including a pulse generator for alternately outputting a pulse to two outputs synchronously with a signal input from an outside and for outputting a pulse train including two pulses having mutual time intervals preset as the pulse to at least one of the two outputs, a set of level shift circuits for level shifting output signals of the two outputs of the pulse generator respectively, and a flip-flop circuit to be set in response to one of output signals of the set of level shift circuits and to be reset in response to the other output signal.
The input signal is level shifted after a conversion into the form of a pulse and is restored to have an original waveform through the flip-flop circuit. Therefore, it is possible to achieve the level shift of the input signal while decreasing a power loss in the level shift circuit. In addition, the input pulse sent to at least one of the set of level shift circuits is the pulse train having two pulses. Therefore, it is possible to suppress the influence of the noise pulse on the turn-on operation or turn-off operation of the power switching element.